NIAGARA FALLS AND VICINITY 65 



great lakes as well as for the maritime species of plants found in the 

 lake district. It must however be borne in mind that this marine 

 invasion was not till after the time of Lake Iroquois, for fresh-water 

 fossils have been found in the beaches of this lake. 



The tilting of the land, which is recorded in the deformed beaches, 

 has not yet ceased, as recent investigations in the lake regions 

 clearly prove. Mr Gilbert has made an extended study of this prob- 

 lem ; and he has been led to the assumption " that the whole lake 

 region is being lifted on one side or depressed on the other, so that 

 its plane is bodily canted toward the southsouthwest, and that the 

 rate of change is such that the two ends of a line lOO miles long and 

 lying in a southsouthwest direction are relatively displaced .4 of a 

 foot in 100 years ". From this it follows that " the waters of each 

 lake are gradually rising on the southern and western shores or 

 falling on the northern or eastern shores, or both ". This implies of 

 course a drowning of the lower courses of all streams entering these 

 lakes from the southwest and an extension of those entering 

 from the northeast. Assuming that the rate and character of 

 change will be constant in the future, the following interesting re- 

 sults have been predicted by Mr Gilbert. The waters of Lake Michi- 

 gan at Chicago are rising at the rate of 9 or 10 inches a century; and 

 ^' eventually, unless a dam is erected to prevent, Lake Michigan will 

 again overflow to the Illinois river, its discharge occupying the 

 channel carved by the outlet of a Pleistocene glacial lake. 

 Evidently the first water to overflow will be that of some high stage 

 of the lake and the discharge may at first be intermittent. Such 

 high water discharge will occur in five hundred or six hundred years. 

 For a mean lake stage such a discharge will begin in about one 

 thousand years, and after one thousand five hundred years there will 

 be no interruption. In about two thousand years the Illinois river 

 and the Niagara will carry equal portions of the surplus water of the 

 great lakes. In two thousand five hundred years the discharge of 

 the Niagara will be intermittent, falling at low stages of the lake^ 

 and in three thousand five hundred years there will be no Niagara. 

 The basin of Lake Erie will then be tributary to Lake Huron, the 

 current being reversed in the Detroit and St Clair channels."^ 



^Gilbert, G. K. Recent earth movements in the great lake region. i8th 

 an. rep't U. S. geol. sur. 1896^97. pt 2. 



